fstring syntax error for python 3.7.13

[russellkune]

Hi,

thank you for the great package!

I noticed that for certain python versions gpn.data has a syntax error:

import gpn.data

gives:

`Traceback (most recent call last):

File "/home/kunesr/miniconda3/envs/scbasset/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3457, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)

File "/scratch/lsftmp/3076066.tmpdir/ipykernel_4206/958883150.py", line 1, in
import gpn.data

File "", line 1
(ref=)
^
SyntaxError: invalid syntax`

It appears to be caused by line 473 in gpn.data

Thanks!